1. Field of the Invention:
This invention relates to an improved polyester support for use in preparing electrostatic transparencies. More particularly, this invention relates to a polyester support with an improved surface applied thereon, one which has substantially improved image and processing capabilities in electrostatic plain paper copy machines.
2. Description of the Prior Art:
As is well-known, applying an image on a support using electrostatic imaging processes requires imparting a uniform electrostatic charge (either positive or negative) to a photoconducting surface which is conventionally, a selenium drum element as the photoconducting surface in this process. A corona discharge system is used to impart this charge to the drum which is then imaged through a lens system to a document or article to be imaged. In areas where the light strikes the photoconducting surface, the charge is dissipated via a grounding process, while the electrostatic image remains intact in the image areas. After this process, toner particles of opposite charge are applied to the drum and clings, via an electrostatic attraction, to the charged areas of the surface. A sheet on which the image is to be recorded, is then passed in contact with the charged drum and another corona discharge applied thereon. As a result, a large portion of the charged toner on the drum is transferred to the sheet. Finally, the toner is fused on this sheet, usually by applying heat, pressure or a combination of both.
Elements useful in preparing transparencies using this electrostatic imaging process are legion in number. Most of these elements employ some sort of transparent support and coated thereon, a toner receptive layer. Many of these elements describe the use of polyester supports such as polyethylene terephthalate as the transparent support since this element is well-known for its dimensional stability which is a great advantage. Toner receptive layers applied on these polyester supports must have a number of special characteristics since it is difficult to coat layers on these supports. Additionally, the toner receptive layers that are applied on to these polyester supports must faithfully record the required image since they usually are employed as overhead transparencies and the like. Thus, the image is greatly enlarged and any deficiency in the recorded image is greatly amplified. Also, when multiple sheets of polyester film are used within standard plain paper copy machines, they must feed into the system in a normal manner. Polyester tends to build up a static charge very easily and thus jams can occur in a machine when polyester sheets are used within the ambit described above. Conventionally, sheets of paper are interleaved between each film and/or a stripe applied to the film surface to enhance the feeding of these films thorugh the electrostatic plain paper copy machines.
There are a host of elements available for use within the system described. These usually employ polyester as the film support suitably treated or subbed to receive a variety of layers applied thereon to record the image and to assist in transfer of the film element through the machinery conventionally used to make said image. Many of these elements can produce good images but process poorly through the transfer machine. Others transfer easily, but have poor resulting images. Thus, it is an object of this invention to prepare an element useful in preparing overhead transparencies in plain paper electrostatic copiers. It is also an object of this invention to prepare an element which not only processes satisfactorily within said plain paper copier but which will have superior image quality.